Compressive strain semiconductor substrates

ABSTRACT

A method for forming a compressively strained semiconductor substrate includes forming a lattice adjustment layer on a semiconductor substrate by forming compound clusters within an epitaxially grown semiconductor matrix. The lattice adjustment layer includes a different lattice constant than the semiconductor substrate. A rare earth oxide is grown and lattice matched to the lattice adjustment layer. A semiconductor layer is grown and lattice matched to the rare earth oxide and includes a same material as the semiconductor substrate such that the semiconductor layer is compressively strained.

BACKGROUND Technical Field

The present invention generally relates to semiconductor devices, andmore particularly to substrates and methods for fabrication that yield acompressive strain employed for formation of semiconductor devices.

Description of the Related Art

Strained silicon and strained silicon-on-insulator (SOI) can provideenhanced properties for semiconductor devices. For example, p-type fieldeffect transistors (PFETs) have improved performance when formed with acompressive strain channel, and n-type field effect transistors (NFETs)have improved performance when formed with a tensile strain channel.Tensile strain devices are easily formed using, e.g., relaxed SiGebuffer layers or SiGe condensation. Compressively strained silicon ismuch more difficult to achieve. Globally compressive strained substratesare not presently known.

SUMMARY

In accordance with an embodiment of the present invention, a method forforming a compressively strained semiconductor substrate includesforming a lattice adjustment layer on a semiconductor substrate byforming compound clusters within an epitaxially grown semiconductormatrix. The lattice adjustment layer includes a different latticeconstant than the semiconductor substrate. A rare earth oxide is grownand lattice matched to the lattice adjustment layer. A semiconductorlayer is grown and lattice matched to the rare earth oxide and includesa same material as the semiconductor substrate such that thesemiconductor layer is compressively strained.

Another method for forming a compressively strained semiconductorsubstrate includes epitaxially growing a first silicon layer on asilicon substrate and introducing an overabundance of phosphine into aprocess gas to form Si₃P₄ within the first silicon layer, the firstsilicon layer having a smaller lattice constant than the siliconsubstrate; growing a rare earth oxide lattice matched to the firstsilicon layer; and growing a second silicon layer by lattice matchingthe second silicon layer to the rare earth oxide such that a latticemismatch provides compressive strain in the second silicon layer.

A compressively strained semiconductor substrate includes a latticeadjustment layer formed on a semiconductor substrate, the latticeadjustment layer including compound clusters formed within anepitaxially grown semiconductor matrix, the lattice adjustment layerincluding a smaller lattice constant than the semiconductor substrate. Arare earth oxide is lattice matched to the lattice adjustment layer. Asemiconductor layer is lattice matched to the rare earth oxide andincluding a same material as the semiconductor substrate such that thesemiconductor layer is compressively strained.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will provide details of preferred embodimentswith reference to the following figures wherein:

FIG. 1 is a cross-sectional view showing a lattice adjustment layerformed on a substrate that alters the lattice constant in accordancewith an embodiment of the present invention;

FIG. 2 is a cross-sectional view showing a rare earth oxide formed onthe lattice adjustment layer and lattice matched to the latticeadjustment layer in accordance with an embodiment of the presentinvention;

FIG. 3 is a cross-sectional view showing a compressively strainedsemiconductor layer formed on the rare earth oxide, the compressivelystrained semiconductor layer being lattice matched to the rare earthoxide in accordance with an embodiment of the present invention; and

FIG. 4 is a block/flow diagram showing a method for forming acompressively strained semiconductor layer in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

In accordance with aspects of the present invention, methods andstructures are provided to form global compressively strainedsubstrates, large embedded substrate sections or local substratesections. In some embodiments, the substrate can include a bulksubstrate or be a multilayered substrate having one or moresemiconductor layers rendered compressive. In one example, of a multiplelayered substrate, a silicon-on-insulator (SOI) substrate can beemployed. Compressive properties can be applied to the semiconductorlayer from the base substrate of the SOI structure.

In useful embodiments, a compound is inserted into a lattice of thesemiconductor material to alter a lattice constant of the semiconductormaterial. The compound can include a material that is a crystallinecompound and is preferably chemically bound with the material of thelattice. The compound can thus form a semiconductor crystal within asemiconductor matrix and affect the lattice constant of the overalllayer.

In one embodiment, Si₃P₄ is provided in a silicon lattice to provide atensily strained layer. Si₃P₄ is formed when an overabundance ofphosphine is provided in a process gas during a fast growing lowtemperature epitaxial silicon process. The Si₃P₄ compound getsincorporated into the silicon lattice and creates a tensile strain(compared to the underlying silicon substrate lattice). Most of thephosphorus is chemically bound. Since there is an overabundance ofphosphorus, the Si₃P₄ containing silicon layer is highly n-doped.However, the bound phosphorus forms crystal clusters of Si₃P₄ within thesilicon to change the lattice constant of the silicon. Si₃P₄ is verythermally stable; however, if grown too thick the Si₃P₄ containingsilicon layer starts to relax, similar to the critical thickness ofthick SiGe layers.

It is to be understood that aspects of the present invention will bedescribed in terms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps can be varied within the scope of aspects of the presentinvention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., lanthanum-yttrium oxide (LaYO₃).These compounds include different proportions of the elements within thecompound, e.g., (La_(x)Y_(1-x))₂O₃ where x is less than or equal to 1,etc. In addition, other elements can be included in the compound andstill function in accordance with the present principles. The compoundswith additional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment”,as well as other variations thereof, means that a particular feature,structure, characteristic, and so forth described in connection with theembodiment is included in at least one embodiment. Thus, the appearancesof the phrase “in one embodiment” or “in an embodiment”, as well anyother variations, appearing in various places throughout thespecification are not necessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein can be interpreted accordingly. In addition, itwill also be understood that when a layer is referred to as being“between” two layers, it can be the only layer between the two layers,or one or more intervening layers can also be present.

It will be understood that, although the terms first, second, etc. canbe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a substrate system 10includes a substrate 12 and a lattice adjustment layer 14. The latticeadjustment layer 14 is formed on the substrate 12 and includes a latticematch altering material. In one embodiment, the lattice adjustment layer14 includes silicon with Si₃P₄ formed therein. The substrate system 10can include a substrate structure including but not limited to a bulksubstrate or a silicon on insulator substrate (SOI).

In one example, the bulk semiconductor substrate 12 may be asilicon-based material. Illustrative examples of Si-based materialssuitable for the bulk semiconductor substrate 12 include, but are notlimited to monocrystalline forms of Si, SiGe, Ge, and multi-layersthereof. The semiconductor substrate system 10 may also be a SOIsubstrate where substrate 12 represents the semiconductor layer on topof a buried dielectric layer of a SOI structure (not shown).

Layer 14 is formed by flowing an overabundance of phosphine into aprocess gas during a fast growing low temperature epitaxial siliconprocess. In useful embodiments, the fast growing low temperatureepitaxial Si₃P₄ containing silicon process can include, by way of anexample, silane at about 600 torr, 600 degrees C. with a phosphine(e.g., partial pressure of around 1.3 torr) (more generally phosphinepartial pressure may be between about 1 and 2 torr) and silane with apartial pressure of about 2-7 torr (e.g., about 4.8 torr for the exampleabove) in nitrogen carrier gas. In other examples, silane ordichlorosilane can be provided at between 200 torr to atmosphericpressure, and temperatures above about 600 degrees C. (e.g., 600-750degrees C.). Other parameters may also be employed. Other examples caninclude, e.g., dichlorosilane at 650-750 degrees C. (preferably about675-700 degrees C.), at a pressure of about 300 torr, with a partialpressure of phosphine about 1.5 torr and dichlorosilane of about 7 torrusing nitrogen as a carrier gas.

The Si₃P₄ compound gets embedded into the silicon lattice of thesubstrate 12 to form layer 14 and creates a tensile strain (compared tothe underlying silicon substrate lattice). Most of the phosphorus inlayer 14 is chemically bound and not electrically active (the overallphosphorus concentration can be about 2-4×10²¹ atoms/cc, with only asmall percentage, e.g., 2-8×10²⁰ atoms/cc being electrically active).

Layer 14 is grown to be in a relaxed state (negligible strain). This canbe achieved by growing a thick layers of silicon containing Si₃P₄. Thestrain relaxation of layer 14 increases with thickness. For example,higher strain is provided in thinner layers of Si₃P₄ clusters in Si anddecreases until fully relaxed at about 2 microns in thickness. Layer 14is grown to about 2 microns to achieve strain relaxation.

The Si₃P₄ clusters form a compound within the Si a lattice of thesemiconductor material to alter a lattice constant of the semiconductormaterial. The compound can include a material that is a crystallinecompound and is preferably chemically bound with the material of thelattice. The compound can thus form a semiconductor crystal within asemiconductor matrix and affect the lattice constant of the overalllayer. Most of the phosphorus is chemically bound.

Referring to FIG. 2, a rare earth oxide (REO) 16 is grown on layer 14.The REO 16 can be epitaxially grown by, e.g., molecular beam epitaxy(MBE) or other epitaxial growth process. In a less preferred embodimentpulsed laser deposition may be employed (PLD).

The terms “epitaxial growth and/or deposition” and “epitaxially formedand/or grown,” mean the growth of a semiconductor material (crystallinematerial) on a deposition surface of another semiconductor material(crystalline material), in which the semiconductor material being grown(crystalline over layer) has substantially the same crystallinecharacteristics as the semiconductor material of the deposition surface(seed material). In an epitaxial deposition process, the chemicalreactants provided by the source gases are controlled, and the systemparameters are set so that the depositing atoms arrive at the depositionsurface of the semiconductor substrate with sufficient energy to moveabout on the surface such that the depositing atoms orient themselves tothe crystal arrangement of the atoms of the deposition surface.Therefore, an epitaxially grown semiconductor material has substantiallythe same crystalline characteristics as the deposition surface on whichthe epitaxially grown material is formed.

The rare earth oxide 16 is lattice matched to layer 14. For latticematching of an epitaxial oxide (e.g., rare earth oxide 16) to thesilicon lattice of layer 14, rare earth oxides with stable stoichiometryand stable cubic crystal structure can be employed. The rare earthoxides can include, for example, gadolinium (III)-oxide (Gd₂O₃),dysprosium (III)-oxide (Dy₂O₃), holmium (III) oxide (Ho₂O₃), erbium(III) oxide (Er₂O₃), thulium (III) oxide (Tm₂O₃), lutetium (III) oxide(Lu₂O₃) or cerium (IV) oxide (CeO₂).

In some embodiments, a ternary oxide can also be employed, e.g.,lanthanum-yttrium oxide ((La_(x)Y_(1-x))₂O₃) or gadolinium-erbium oxide((Gd_(x)Er_(1-x))₂O₃), etc. may be employed. The ternary oxidescrystallize in a cubic form. In one embodiment, (La_(x)Y_(1-x))₂O₃ maybe employed where x can be between about 0.3 and 0.35, and preferablyabout 0.33. The lanthanum-yttrium oxide includes a lattice constant thatis about two times that of Si permitting lattice matching. The yttriumhas to be the majority compound to ensure a cubic lattice is formed, forthe yttrium-lanthanum-oxide system ((La_(x)Y_(1-x))₂O₃).

In accordance with aspects of the present invention, layer 14 and layer16 are lattice matched by an epitaxial growth process. Layer 14 includesa lattice constant that is smaller than the lattice constant of theunderlying silicon substrate 12 due to the effects of the Si₃P₄ formedin layer 14.

Referring to FIG. 3, a semiconductor layer 18 is epitaxially grown onthe rare earth oxide 16. In one embodiment, the semiconductor layer 18includes silicon. Since the rare earth oxide 16 is epitaxially grown onthe layer 14, the rare earth oxide 16 has a lattice constant that issmaller than that of silicon (substrate 12). This slight latticemismatch results in a compressive strain in the silicon of layer 18.Using this structure, a SOI substrate system 10 is provided with thesubstrate and layer 14 forming a base substrate, the rare earth oxide 16forming a buried dielectric and the semiconductor layer 18 forming thesemiconductor portion.

The substrate system 10 may be employed for the formation of PFETs orother components that would benefit from a compressively strainedsubstrate. It should understood that the structure 10 may be formedacross an entire wafer or chip or over smaller sections or portions ofthe wafer or chip.

In accordance with aspects of the present invention, accommodatinglattice constants can be provided by selecting an appropriate rare earthoxide. The rare earth oxide may include different compounds or compoundswith different stoichiometry. Table 1 shows an illustrative example ofstoichiometric matching using (La_(x)Y_(1-x))₂O₃.

TABLE 1 Stoichiometry for tensile silicon containing Si₃P₄ latticematched epitaxial oxide layer ((La_(x)Y_(1−x))₂O₃) Si₃P₄ (Si:C % LatticeTwice the lattice x-value for equivalent) constant [A] constant (2[A])(La_(x)Y_(1−x))₂O₃   0% 5.431  10.862 0.33  0.5% 5.421 10.84 0.31  1.0%5.411 10.82 0.288 1.25%  5.406 10.81 0.272 1.5% 5.402 10.80 0.262   2%5.392 10.78 0.236

Here, Si₃P₄ atomic percent is expressed as an equivalent atomic percentas provided in a percent of C in Si:C as measured by high-resolutionx-ray diffraction (HRXRD). The lattice constant [A] is the latticeconstant of the Si₃P₄ containing silicon layer 14 that is matched by(La_(x)Y_(1-x))₂O₃ for a given value of x. The lattice constants areexpressed in Angstroms. For other semiconductor systems, differentepitaxial oxides can be employed to lattice match the Si₃P₄ containingsilicon layer 14. Some examples can include gadolinium (III)-oxide(Gd₂O₃), dysprosium (III)-oxide (Dy₂O₃), holmium (III) oxide (Ho₂O₃),erbium (III) oxide (Er₂O₃), thulium (III) oxide (Tm₂O₃), lutetium (III)oxide (Lu₂O₃), cerium (IV) oxide (CeO₂) or ternary compounds, asfollows.

TABLE 2 Stoichiometry for tensile Si₃P₄ containing Silicon latticematched epitaxial oxide layers Twice the Si₃P₄ Lattice lattice (Si:C %constant constant (La_(x)Y_(1-x))₂O₃ (Gd_(x)Er_(1-x))₂O₃(Nd_(x)Er_(1-x))₂O₃ (Nd_(x)Gd_(1-x))₂O₃ (La_(x)Er_(1-x))₂O₃ equivalent)[A] (2[A]) La % Y % Gd % Er % Nd % Er % Nd % Gd % La % Er % 0.5% 5.42110.84 31 69 55.1 44.9 11.8 88.2 55.1 44.9 1.0% 5.411 10.82 28.5 71.551.3 48.7 4.4 95.6 32.8 67.2 1.25%  5.406 10.81 27.2 72.8 100 49.4 50.6100 31.6 68.5 1.5% 5.402 10.80 26.2 73.8 97.7 2.3 47.9 52.1 30.6 69.42.0% 5.392 10.78 23.6 76.4 90 10 44.1 55.9 28.2 71.8

The rare earth oxides include a cubic epitaxial oxide layer, which isusable to form compressive silicon in a SOI structure.

Referring to FIG. 4, methods for forming a semiconductor substrate withcompressive strain are illustratively shown. In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

In block 102, a lattice adjustment layer is formed on a semiconductorsubstrate by introducing a material into the lattice adjustment layer.The lattice adjustment layer includes a smaller lattice constant thanthe semiconductor substrate by the formation of a silicon-containingcompound, e.g., Si₃P₄.

In block 104, an overabundance of phosphine is introduced into processgas while forming epitaxial silicon for the lattice adjustment layer onthe semiconductor substrate. This forms clusters or crystals of Si₃P₄ inthe lattice adjustment layer. The semiconductor substrate includessilicon and provides a layer for epitaxial growth to form the Si₃P₄containing lattice adjustment layer. In block 106, the latticeadjustment layer is relaxed (negligible strain). The relaxation ofstrain in the lattice adjustment layer can be provided by forming thelattice adjustment layer to a large enough thickness to provide at leasta relaxed strain upper portion of the lattice adjustment layer.

In block 108, a rare earth oxide is grown on the lattice adjustmentlayer and lattice matched to the lattice adjustment layer. The rareearth oxide may include binary oxides, such as, e.g.,gadolinium(III)-oxide (Gd₂O₃), dysprosium(III)-oxide (Dy₂O₃),holmium(III) oxide (Ho₂O₃), erbium (III) oxide (Er₂O₃), thulium (III)oxide (Tm₂O₃), lutetium(III) oxide (Lu₂O₃) or cerium (IV) oxide (CeO₂),etc. or ternary oxides including a rare earth metal, such as e.g., Gd,Er, Nd, La and Y forming oxides such as, e.g., lanthanum-yttrium oxide((La_(x)Y_(1-x))₂O₃), gadolinium-erbium oxide ((Gd_(x)Er_(1-x))₂O₃),neodymium-erbium oxide ((Nd_(x)Er_(1-x))₂O₃), neodymium-gadolinium oxide((Nd_(x)Gd_(1-x))₂O₃), lanthanum-erbium oxide ((La_(x)Er_(1-x))₂O₃),etc.

In block 110, the rare earth oxide is lattice matched to the latticeadjustment layer by selecting a stoichiometry (e.g., adjusting x) of therare earth oxide.

In block 112, a semiconductor layer is grown on the rare earth oxide andlattice matched to the rare earth oxide. The semiconductor layerincludes a same material as the semiconductor substrate. The slightlattice difference causes the semiconductor layer to be compressivelystrained.

The semiconductor layer with compressive strain may be formed over theentire chip or wafer or sections of portions of the wafer or chip. Inblock 114, the substrate with the compressively strained semiconductorlayer can be employed to form devices, e.g., field effect transistors(FETs) of any type (e.g., FinFETs, vertical FETs, nanowires, planarFETs, etc.). Other components can also be formed in the compressivesemiconductor layer. The compressive semiconductor layer can be employedwith other regions having tensile strain or no strain as well. In someembodiments, the substrate having a compressively strained semiconductorlayer can be provided as a material or product to semiconductorfabrication foundries for production of semiconductor devices.

Having described preferred embodiments for compressive strainsemiconductor substrates (which are intended to be illustrative and notlimiting), it is noted that modifications and variations can be made bypersons skilled in the art in light of the above teachings. It istherefore to be understood that changes may be made in the particularembodiments disclosed which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims.

What is claimed is:
 1. A method for forming a compressively strainedsemiconductor substrate, comprising: forming a lattice adjustment layeron a semiconductor substrate by forming compound clusters within anepitaxially grown semiconductor matrix, the lattice adjustment layerincluding a different lattice constant than the semiconductor substrate;growing a rare earth oxide lattice matched to the lattice adjustmentlayer; and growing a semiconductor layer lattice matched to the rareearth oxide and including a same material as the semiconductor substratesuch that the semiconductor layer is compressively strained.
 2. Themethod as recited in claim 1, wherein forming the lattice adjustmentlayer includes introducing an overabundance of phosphine into a processgas while forming epitaxial silicon on the semiconductor substrate. 3.The method as recited in claim 1, wherein forming the lattice adjustmentlayer includes forming the lattice adjustment layer with negligiblestrain.
 4. The method as recited in claim 1, wherein forming the latticeadjustment layer includes forming the lattice adjustment layer to athickness that includes negligible strain.
 5. The method as recited inclaim 1, wherein the rare earth oxide is selected from the groupconsisting of gadolinium(III)-oxide, dysprosium(III)-oxide, holmium(III)oxide, erbium (III) oxide, thulium (III) oxide, lutetium (III) oxide andcerium (IV) oxide.
 6. The method as recited in claim 1, wherein the rareearth oxide includes a ternary compound including a rare earth metalselected from the group consisting of gadolinium, erbium, neodymium,lanthanum and yttrium.
 7. The method as recited in claim 1, wherein thelattice constant of the rare earth oxide is matched to the latticeadjustment layer by selecting a stoichiometry of the rare earth oxide.8. A method for forming a compressively strained semiconductorsubstrate, comprising: epitaxially growing a first silicon layer on asilicon substrate and introducing an overabundance of phosphine into aprocess gas to form Si₃P₄ within the first silicon layer; growing a rareearth oxide lattice matched to the first silicon layer; and growing asecond silicon layer by lattice matching the second silicon layer to therare earth oxide such that a lattice mismatch provides compressivestrain in the second silicon layer.
 9. The method as recited in claim 8,wherein forming the first silicon layer includes forming the firstsilicon layer with negligible strain.
 10. The method as recited in claim8, wherein forming the first silicon layer includes forming the firstsilicon layer to a thickness that provides negligible strain.
 11. Themethod as recited in claim 8, wherein the rare earth oxide is selectedfrom the group consisting of gadolinium(III)-oxide,dysprosium(III)-oxide, holmium(III) oxide, erbium (III) oxide, thulium(III) oxide, lutetium (III) oxide and cerium (IV) oxide.
 12. The methodas recited in claim 8, wherein the rare earth oxide includes a ternarycompound including a rare earth metal selected from the group consistingof gadolinium, erbium, neodymium, lanthanum and yttrium.
 13. The methodas recited in claim 8, wherein the rare earth oxide is lattice matchedto the first silicon layer by selecting a stoichiometry of the rareearth oxide.
 14. A compressively strained semiconductor substrate,comprising: a lattice adjustment layer formed on a semiconductorsubstrate, the lattice adjustment layer including compound clustersformed within an epitaxially grown semiconductor matrix, the latticeadjustment layer including a smaller lattice constant than thesemiconductor substrate; a rare earth oxide lattice matched to thelattice adjustment layer; and a semiconductor layer lattice matched tothe rare earth oxide and including a same material as the semiconductorsubstrate such that the semiconductor layer is compressively strained.15. The substrate as recited in claim 14, wherein the lattice adjustmentlayer is relaxed.
 16. The substrate as recited in claim 14, wherein therare earth oxide is selected from the group consisting ofgadolinium(III)-oxide, dysprosium(III)-oxide, holmium(III) oxide, erbium(III) oxide, thulium (III) oxide, lutetium (III) oxide and cerium (IV)oxide.
 17. The substrate as recited in claim 14, wherein the rare earthoxide includes a ternary compound including a rare earth metal selectedfrom the group consisting of gadolinium, erbium, neodymium, lanthanumand yttrium.
 18. The substrate as recited in claim 14, wherein thelattice adjustment layer includes a thickness of at least 2 microns.